If it's the IOM (TT time sounds fecking cool ) where would you like to throw them in? I maybe be able to sort enough visitor berths out at fleetwood so all can go out on in one go, but this isn't the shortest point if that's what your after? Jono's home ground could be another good spot or even Liverpool marina?
If it's a case of going off slips and straight out then it's Knott end (£8 if the ferry man catches you) slip up around morcambe bay slips unless you have a permit for wales or the wirral.